1. Field of the Invention
The present invention relates to a switched reluctance motor (SRM), and more particularly to a driving apparatus of the SRM for reducing a radial force which is generated when the SRM is driven.
2. Description of the Prior Art
In general, switched reluctance motors (SRMS) include, as shown in FIG. 1, a stator 2 and a rotor 4, wherein the stator 2 has three pairs of poles +A and -A, +B and -B, and +C and -C (or, salient pole C) on which A phase coil 6, B phase coil 8, and C phase coil 10 are respectively wound.
A driver for the SRM thus constructed consists of, as shown in FIG. 2, a smoothing capacitor C for producing a direct current (DC) voltage, a plurality of switching elements Q1 to Q6 for applying the voltage to the respective phase coils 6, 8, and 10, 6 diodes D1 to D6 for feedback of a back electromotive force created at the time of turning-off of the respective switching elements Q1 to Q6 after applying the voltage to each said phase coil.
The switching operation of the A-phase switching elements Q1 and Q2 may be controlled by a signal produced from a gate signal generating unit. This unit includes, as shown in FIG. 3, an oscillator 12 which outputs a Pulse Width Modulated (PWM) signal, an AND logic gate 16 which produces a logic product of said produced PWM signal and a position information signal available from an A phase position sensor 14 when the rotor 4 faces with A phase pole of the stator 2, wherein the signal from the AND logic gate 16 is applied to an upper A phase switching element Q1, and wherein the position information signal from the A phase position sensor 14 is applied to a lower A phase switching element Q2.
An application of a power to the A phase of the SRM may be made by giving operational signals to the gate of A phase-related switching elements Q1, Q2. The activated switching elements Q1, Q2 allow electric current to flow through the A phase coil of the stator 2, resulting in magnetization of the poles +A and -A of the stator. Such magnetized poles pull the rotor 4 positioned near the A phase pole.
B and C phase coils 8 and 10 also operate as in A phase-related action, similarly, wherein the order of A, b and C phase for the magnetization of the stator 2 is maintained, by which the motor can continue to rotate.
However, when the switching elements are turned off, the conventional SRM as described above generates a radial force causing a loud noise. In particular, the greater radial force is generated when both upper and lower switching elements are turned off at the same time.
Meanwhile, there is disclosed in Japanese laid open utility model application No. Hei 2-123997 another driver for the SRM. In the driver which conducts in a predetermined order phase-windings provided with each phase pole to create torque applied to salient pole, the driver includes position detecting means for detecting two relative positions of a salient pole of a rotor, which are determined in advance, time measuring means for measuring a time period lapsed after the detection of initial relative positions by the position detecting means, and conduction control means that initiates the conduction to said phase windings at earlier detected time point and stops conducting to the phase windings at later detected time point.
Accordingly, when rotary speed of SRM is reduced, a rotary angle of initiated conduction at an upper winding moves toward a forward angle and when the rotary speed is increased, the rotary angle of the initiated conduction moves toward a retarded angle, to thereby restrict changes of rotary speed according to load variation.